For most of the Middle Ages, canon law’s position toward the Jews of Latin Christendom was straightforward: they were to be marginalized, but not expelled. Over the course of the fourteenth and fifteenth centuries, however, jurists began to question whether canon law might indeed require the expulsion of Jews. This question turned on the interpretation of an ecumenical decree, Usurarum voraginem, which had been drafted in response to Christian moneylending, but whose ambiguous phrasing took on new meaning as a result of shifting political dynamics and new trends in canonistic jurisprudence. Ultimately, even a reigning pope would come down in favor of an expansive reading of the decree, rupturing a tradition of papal resistance to Jewish expulsion that had endured for nearly a thousand years. By tracing jurists’ debates over the meaning of the decree alongside the response of secular and ecclesiastical authorities, this paper explores the interaction between legislative intent, legal interpretation, and the expulsion of Jews in the late Middle Ages.